PROJECT SUMMARY/ABSTRACT Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease. Although surgery is the primary curative option, more than 75% of patients are ineligible and respond only transiently, to chemo- and radiotherapy (RT). New and effective treatment option is desperately needed. Recently, the development of RT as a therapeutic modulator for systemic treatment such as immunotherapy has cast the use of radiation into a pivotal role in the management of PDAC, inspiring several clinical trials. Given these early clinical studies, there is a compelling need to establish a clinically-relevant experimental system to further advance our understanding of the role of RT . A genetically engineered mouse model would provide a powerful model system to dissect the radiobiological mechanism of RT. The majority of PDAC (>90%) has somatic mutations in the KRAS signaling pathway. Importantly, using publicly available gene expression datasets, we found that TWIST1 is overexpressed in human PDAC which represents the most aggressive ?squamous variant? subset of pancreatic cancer. We hypothesize that the generation of a pancreas specific Kras-Twist1 autochthonous mouse model provides an innovative resource to determine how TWIST1 contributes to tumorigenesis and progression. As for the important pre-clinical research to study treatment response of the murine PDAC model, radiation needs to mimic RT used for human. Such advanced technology is now available in the form of the small animal radiation research platform (SARRP) pioneered at our group. The SARRP is equipped with on- board cone-beam CT (CBCT) to guide irradiation. Recognizing that CBCT imaging is inadequate for localizing the PDAC growing in a low image contrast tissue environment, we innovated bioluminescence tomography (BLT) on board the SARRP to complement CBCT guidance. As an important complement, we engineered inducible Twist1-Luc gene expression in our PDAC model such that the disease progression can be monitored by bioluminescence imaging and the spontaneous PDAC can also be localized with BLT for radiation delivery. In response to PAR-16-176, we propose to integrate the inducible Kras-Twist1-Luc PDAC model and the CBCT-BLT-guided SARRP to establish a novel experimental system that will enable researchers to evaluate and develop new treatment options for human squamous variant PDAC in ways that have not been feasible before. To achieve this goal, we propose to (1) develop an inducible Twist1 transgenic autochthonous PDAC model and determine if Twist1 overexpression can cooperate with KrasG12D to accelerate PDAC tumorigenesis; (2) advance the targeting and quantitative imaging capabilities of the BLT-guided SARRP system for the PDAC model. The success of this proposal will provide a model system with strong pre-clinical foundation to study the effectiveness of combining radiation and other therapeutic agents for PDAC in great translational opportunity.